1. Field of the Invention
The invention relates to a three knife trimmer, comprising a front knife and two lateral knives which are driven by a drive device such that they perform on a material to be trimmed a front cut and at least one lateral cut with phase displacement.
2. Description of the Related Art
Three knife trimmers for cutting or trimming three sides of printed products, for example, books, brochures and the like, have been known in the art for some time. For carrying out the cutting process, the material to be cut is conveyed onto a cutting table, aligned on the cutting table underneath the knives, and secured by a pressing plate or the like on the cutting table. By means of the two lateral knives the top and bottom sides of the material are cut at the same time. Prior to this, or subsequent thereto, the front side is cut by the front knife in an additional working step. The trimmed material is moved automatically out of the cutting area and is guided away from the three knife trimmer, for example, by means of a conveyor belt. In these three knife cutting machines or trimmers, the cuts are thus always performed in a single cutting station. Since the material to be cut must be aligned only once, significant advantages result relative to three knife cutting machines with two cutting stations. In order for the front and lateral knives not to collide, the front cut and the lateral cuts are performed with phase displacement.
A three knife trimmer or cutting machine of the aforementioned kind is, for example, known from German patent application 32 01 836. It has a drive device for the knives which comprises a so-called guide gear unit and a so-called operational gear unit upstream thereof. The operational gear unit is formed by a gear wheel unit with a gear ratio which changes during one revolution of a single revolution shaft. A further three knife cutting machine is described in Swiss patent application 537 260. Here, the drive for the knives is realized by a driven single revolution shaft supported within the machine body. On the ends of the single revolution shaft a crank is arranged, respectively, having crank pins which engage a connecting rod, respectively. For driving the front blade a universal joint rod is also provided which is said to make possible a replacement of the conventional two-sided knife pull by a single-sided knife pull. These three knife trimmers are comparatively complex with respect to their configuration and, in particular, the configuration of the drive.